Knitted compressive stretch fabrics,and method and apparatus for the manufacture thereof

ABSTRACT

A KNITTED COMPRESSIVE STRETCH FABRIC HAVING A PORTION MADE OF A LIGHTER AND A HEAVIER STRETCH YARN WHEREIN THE LIGHTER YARN IS THE BASIC YARN IN THAT PORTION AND THE HEAVIER STRETCH YARN IS ARRANGED IN PRE-SELECTED COURSES OF THE LIGHTER YARN IN SAID PORTION AND IN MINIMALLY TENSIONED CONDITION DURING KNITTING. STRUCTURE AND MANUFACTURING OR PROCESS TECHNIQUES ARE ALSO PROVIDED WHEREIN FLUID UNDER PRESSURE, FOR EXAMPLE AIR, IS DIRECTED AT THE HEAVIER YARN, DURING KNITTING, SO AS TO MINIMIZE THE TENSION PRODUCED THEREIN, DURING KNITTING OF THAT YARN INTO THE FABRIC BY POSITIONING THE HEAVIER YARN WITH RESPECT TO THE FLOATED NEEDLES TO ASURE PROPER FLOATING WITHOUT SIGNIFICANTLY STRETCHING OR IMPARTING ANY TENSION TO THE HEAVIER YARN.

March 13, 1973 KNIT A. BURLESON 3,720,078 ESSIVE STRETCH FABRICS ETHOD AND APPARATUS FOR THE Filed March 16, 1970 R m m. V W

ATTORNEYS March 13, 1973 A. BURLESON KNITTED COMPRESSIVE STRETCH FABRICS AND METHOD EOF AND APPARATUS FOR THE MANUFACTURE THEIR Filed March 16, 1970 2 Sheets-Sheet 2 I I INVENTOR fifiAO/v 5024550 1 ,QQ QZAAM ATTORNEYS United States Patent flice 3,72,fi78 Patented Mar 13, 1973 3,720,078 KNITTED COMPRESSEVE STRETCH FABRICS, AND METHOD AND APPARATUS FOR THE MANUFACTURE THEREOF Aaron Burleson, Burlington, N.C., assignor to Burlington Industries, The, Greensboro, N13. Filed Mar. 16, 1970, Ser. No. 20,007 Int. Cl. DtMb 9/18, 9/46, 15/50 U.S. Cl. 66-433 7 Claims ABSTRACT OF THE DISCLGSURE A knitted compressive stretch fabric having a portion made of a lighter and a heavier stretch yarn wherein the lighter stretch yarn is the basic yarn in that portion and the heavier stretch yarn is arranged in pre-selected courses of the lighter yarn in said portion and in a minimally tensioned condition during knitting. Structure and manufacturing or process techniques are also provided wherein fluid under pressure, for example air, is directed at the heavier yarn, during knitting, so as to minimize the tension. produced therein during knitting of that yarn into the fabric by positioning the heavier yarn with respect to the floated needles to assure proper floating without significantly stretching or imparting any tension to the heavier yarn.

This invention relates to garments made of compressive stretch fabrics. More particularly, it relates to circularly knit compressive, stretch fabrics, such as panty hose, and wherein two different types of stretch yarn are utilized in the garment, for example, in the panty or girdle portion for purposes of providing a better fit and a better foundation, and over a greater range of sizes.

While this invention was developed to have special application to the girdle portion of the now popular panty hose, it will be appreciated that it will have application to other types of compressive, stretch, support garments for men or women, and that it may also be applied to the thigh or other parts of stockings. I

It is known to produce panty hose blanks on circular knitting machines by producing an ordinary stocking leg and then, in place of the welt, knitting an extra long welt to form the panty portion. The welt is slit on one side and joined to a similar blank as by seaming, preferably with the insertion of suitable crotch structure or pieces to improve the fit, thus forming conventional panty hose. Preferably also, the panty hose is constructed of stretch yarns to permit fitting a number of leg and foot sizes, for example, by using an elastic stretch nylon yarn, such as Superloft, of the false twist texturized type in the leg and by using some S-uperloft yarn in a mixture with a stretch non-foam elastomeric polyurethane yarn such as spandex, to improve fit on the body of the wearer and if desired, to provide a certain amount of girdle-type holding power (see the co-pending US. patent application of Burleson and Butler, Ser. No. 836,997, filed June 26, 1969, now US. Pat. 3,651,670 issued Mar. 28, 1972). As will be understood, spandex is the generic designation for nonfoam elastomeric polyurethane yarn (sheathed with nylon or bare). An example of spandex that may be used in panty hose would be about 140 denier, and of the Superloft about 2/ 30 denier.

In practice, it has been diflicult to fit a number of sizes with a single product and provide the desired stretch and power. The reason for this is that in knitting the highly stretchable polyurethane yarn (either of the bare or nylon covered type), it is necessary to knit it under relatively high tension since tension is developed in removing the yarn from its package, pulling it to the needles and working it into the fabric, i.e., the yarn is tensioned as a necessary adjunct of the knitting operation. To some extent, tension in removing the spandex yarn from the package can be reduced by using roll-ofi' structure heretofore proposed. However, there is still a relatively large amount of tension at the needles causing the yarn to be stretched a fair amount when it is knit into the fabric.

If the heavier stretch yarn (e.g. spandex) could be knit in a substantially tension free condition, it would be desirable to float it in according to the conventional fabric construction illustrated in FIG. 2 of the accompanying drawing since with conventional stitching fewer courses are needed to provide a finished garment and less yarn is therefore used to provide the desired stretch and covering power (for example, 810 courses will provide 31 inches of stretch fabric). Because it has been necessary to knit the heavier yarn (e.g. spandex) under tension, a positive floating has been used to knit the heavier yarn in the fabric according to the float structure shown in FIG. 3. (It is understood that presently available devices cannot knit the heavier stretch yarn under tension according to the construction of FIG. 2 since that yarn, being under tension, while knit, will not permit stretching of 810 courses to 31 inches, it being found that the heavier stretch yarn limits the stretch capabilities of the lighter stretch yarn (e.g. Superloft) when the heavier yarn is knitted under tension.)

A prior art method of achieving the floating of a highly stretchable yarn consists in applying sufiicient tension to the yarn so that the yarn will lie along a chord of an arc, the are being defined by the perimeter of the circle of needles extending from a needle, the hook of which holds one portion of the yarn to a spaced needle holding the other portion of the yarn with the intervening needle or needles lying along the arc and the chord along which the floated portion of the yarn lies extending along a straight line between the needles in the hooks of which the yarn is placed. While this method has resulted in the formation of a fabric having relatively few knitting defects as a result of a small chance of the intervening needles knitting in a portion of the yarn that is intended to be floated, the necessity of drawing the yarn to be coincident with a chord of the above mentioned are has resulted in the production of undesirable tension in the yarn thus reducing the stretch potential of the finished garment.

When the heavier stretch yarn is knitted in under tension in the fabric construction shown in FIG. 3, it is possible to obtain 30-31 inches of stretch fabric with 1240 courses and this has been reasonably satisfactory. It would be more desirable, however, if the same stretch and power characteristics could be provided by fewer courses.

Accordingly, it is a primary objective of this invention to provide novel structures, methods and techniques for knitting an elastic, stretch yarn under considerably less tension than heretofore achieved, in combination with a conventionally stitched fabric made of a different elastic, stretch yarn to provide a stretch garment with optimum stretch and power characteristics. A more specific object resides in the provision of novel structures, methods and techniques to adapt conventional circular knitting machines to form stretch garments, of the type referred to, wherein the heavier stretch yarn is knitted into the fabric under minimal tension, and the lighter stretch yarn is knitted in a conventional stitch pattern.

A further object resides in the provision of novel, knitted stretch garments, of the type referred to, having greater stretch potential and utilizing fewer courses than conventional stretch garments. More specifically, the garment construction includes the main, lighter stretch yarn knit in conventional courses and with the heavier stretch 3 yarn knitted in preselected courses of the first yarn and under minimal tension whereby it will have substantially its full stretch capability. Thus, a better product may be provided and over-all savings may be achieved since equal or greater stretch potential is realized from fewer courses.

In the illustrative embodiment of the invention, described in detail hereinbelow, the tension in the heavier yarn is minimized by providing an air jet adjacent the knitting needles and operative, whenever the heavier yarn is being knit, to blow air at relatively low pressure at the yarn. And in an exemplary fabric construction, embodying the invention, the heavier stretch yarn is arranged in alternate courses of the lighter stretch yarn with a stitch loop every third wale and floating behind the lighter yarn in the intervening wales. It will be appreciated, however, that other arrangements of the heavier yarn will be possible and still be within the scope of the invention.

The foregoing and other objects and advantages of the invention will appear from the following description of the preferred embodiments illustrated in the accompanying drawings, wherein:

FIG. 1 is a fragmentary, diagrammatic front view of a hosiery-girdle type panty hose to which the invention may be applied;

FIG. 2 is a diagrammatic view of the outer face of a stretch fabric, of the type under consideration, wherein the heavier stretch yarn is under relatively high tension and is floated behind the knitting needles in certain of the wales;

FIG. 3 is a diagrammatic view, corresponding to FIG. 2, and showing the heavier stretch yarn being positively floated in front of the needles, according to a previously proposed arrangement;

FIG. 4 is a diagrammatic view, corresponding to FIGS. 2 and 3, and showing an exemplary construction of the present invention wherein the heavier stretch yarn is floated behind the wales of the body yarn and is under minimum tension conditions;

FIG. 5 is a diagrammatic plan view of a circular knitting machine, simplified for purposes of illustration, and with certain parts not shown for convenience, and showing an exemplary embodiment of the invention; and

FIG. 6 is a diagrammatic view illustrating and indicating knitting of a fabric according to the invention.

Referring now to the drawings, wherein similar reference numerals have been used to designate similar parts, FIG. 1 illustrates a hosiery-girdle type panty hose to which the present invention may be applied. The panty hose, as is understood, comprises two seamless hose 22, 24 each having an upper portion 26, 28 adapted to form the compressive girdle portion when the two hose are joined together. As is conventional practice, the tubular upper portions 26, 28 of a pair of hose are slit longitudinally from their upper edges along the intended inner junctures. The two hose are then joined directly together along the edges formed by the slit except in the crotch area. In that area, the two hose are joined by the diamond shaped crotch panel 30 with the edges formed by the slits in the hose being sewn to the crotch panel 30, as is understood.

It will be appreciated that in the manufacture of panty hose, of the kind having two types of stretch yarn in the panty-girdle portion, as referred to above, it has been desired to knit the conventional float stitch pattern shown in FIG. 2 for the heavier elastic yarn 34 in the panty or girdle portion. As will be seen, in that pattern, the lighter body yarn 32 (e.g. Superloft) is knitted in the various courses A, B, C in conventional stitching and the heavier stretch yarn 34 (e.g. spandex) is arranged in alternate courses of the body yarn 32 with a stitch loop in every third wale (e.g. W and W and floating across intervening wales. It has been found, however, that the tension developed in the yarn 34 during knitting and floating it behind the knitting needles has caused defects and resulted in the formation of a fabric with low stretch properties.

In order to avoid the problem of trying to float the relatively thick yarn 34 behind the needles, manufacturers have switched to the positive float structure illustrated in FIG. 3 wherein the heavier yarn 34 is fed in front of the needles, as shown. This construction, however, has also been objectionable because it takes more courses of yarn to provide the same amount of stretch, as will be evident.

The problem has been solved according to the present invention by minimizing tension on the heavier yarn 34 while it is being floated across the intervening needles, as indicated in FIG. 4. Thus, it will be seen that the fabric construction of FIG. 4 corresponds to the conventional fabric construction shown in FIG. 2 except that the heavier stretch yarn 34 is under considerably less tension. This provides a fabric with much greater stretch potential, for example, about 40% more stretch than is currently obtainable. In the exemplary construction shown in FIG. 4, the heavier yarn will be arranged in alternate courses B", D", etc., with a stitch loop every third wale, W" W], W" etc. and floating across intervening wales W" W" W W" etc. Other arrangements, however, within the scope of the invention, will be suggested to those skilled in the art and still provide an improved garment construction. In achieving this result, the present invention contemplates the provision of means for reducing the tension in the heavier stretch yarn while it is being knitted and floated in the fabric. In the exemplary arrangement of this means shown in FIG. 5, a nozzle 36 or air jet is shown as being provided adjacent the knitting station 38 of a conventional circular knitting machine 40, for example, of the multi-feed type and designed to knit two courses per revolution. Only the heavier stretch yarn 34 is shown in FIG. 5 being fed to conventional latch needles 42 by a conventional yarn feeding finger 44. In FIG. 6, the body stretch yarn 32 is shown as being fed by yarn feeding finger 46 to the needles.

To produce the exemplary fabric construction shown in FIG. 4, it will be appreciated that when knitting the heavier stretch yarn into the fabric, every third needle will be elevated sufficiently high at the feeding station 48 so as to catch both yarn 32 and yarn 34 within the hook and latch while the intervening two needles will be raised a lesser height so as only to catch the body yarn 32, as indicated in FIG. 6.

The movement of the needles 42 will be from right to left, as viewed in FIGS. 5 and 6, as will be evident. Thus, 7

after the needles have passed through the feed station 48 they will then pass to the knitting station 38, and the latches of the needles will be closed, as understood.

In the illustrative embodiment of FIGS. 5 and 6, the nozzle 36 is shown as being provided adjacent the knitting station 38, and in communication with a source of fluid pressure 50, whereby fluid under pressure, for example, air will be blown continuously on the needles during the knitting operation. The air jet will be controlled to blow air only during the period when the heavier yarn 34 is being knitted, that is, only during formation of the panty body or girdle portion.

Thus, when knitting the heavier yarn 34 in the panty body or girdle portion, that yarn will be blown free from the needles, as illustrated in FIGS. 5 and 6. The air pressure necessary to satisfactorily accomplish this objective has been found to be relatively low, for example, only about eight pounds per square inch line pressure should be sufficient. And, it will be appreciated that the size and shape of the nozzle 36 may be varied within the scope of the invention.

Initial indications are that substantial reduction in manufacturing costs can be realized by the present invention since the conventional fabric construction for the lighter stretch yarn can be utilized, thereby saving yarn in requiring the knitting of fewer courses, and also saving actual knitting time. It may also be possible to use bare or unsheathed spandex yarn for the heavier stretch yarn 34, permitting still further savings, as will be appreciated.

While the use of the air jet 36 of the invention admittedly will result in placing slightly more of the heavier yarn 34 per course into the fabric, since that yarn is under less tension than in previous constructions, overall savings are nevertheless achieved by reason of being able to meet wearing and stretch requirements by knitting fewer courses.

It will be appreciated that the present invention will provide other advantages than those mentioned. For example, in' knitting the heavier 34 and lighter 32 stretch yarns in the panty body or girdle portion, it has been necessary heretofore to eliminate the heavier yarn from the thigh area and knit only the lighter yarn 32 in the thigh area because tension developed in the heavier yarn would not permit obtaining enough stretch for the wearer to use the garment in the thigh area. This objection is overcome with the present invention inasmuch as the heavier yarn may be knitted into the fabric under substantially less tension providing more unstretched heavy yarn in the fabric thereby permitting more stretch potential and providing more power.

It might be noted that the problem of knitting the heavier stretch yarn under relatively large tension and trying to float while under tension has been so severe that attempts have been made to provide needles with offset hooks to facilitate floating. In practice, however, this has not worked satisfactorily either, and defective fabric has resulted, for example, by missing floats and knitting in. With the present invention, however, it is possible to use only ordinary needles and produce a superior product.

As further explanation of the present invention, it will be noted that in conventional floating using spandex yarn it is necessary to apply suflicient tension to the spandex yarn so that it will form a chord of an are between two needles in whose hooks it is placed and will be carried behind the intervening needles it is to be floated across. Therefore, substantial tension is necessary in a conventional floating process. As an example, the typical spandex yarn which has been double-covered with nylon has a maximum elongation of approximately 200%.

As it is necessary to use approximately grams tensioning on this particular spandex yarn while it is being knitted to make it float properly behind the intervening needles, upon examining the stress-strain curve of this particular yarn it has been found that approximately /2 of the 200% elongation is used up with this 5 grams tensioning. Therefore, the 'knitted stitch with the spandex yarn as compared with the knitted stitch of the base yarn can only stretch an additional 100% in relation to the maximum stretch of the base stitch of nylon.

Under this condition then the nylon yarn could only be knitted to a looseness of 100% which is equal to the maximum spandex stretch left since both of these yarns would be in the needle hook and would be carried down across the sinker to form the stitch. Although this 100% stitch length, so called, might be satisfactory in some instances, in other instances it is necessary to have a stitch length of nylon greater than that 100% amount. If this is the case, another problem presents itself wherein at the point in the knitting cycle where the sinkers are withdrawn and the sinker tension is removed, the spandex immediately contracts and clamps tightly around the needle shank. The base nylon yarn, having less contraction force, protrudes beyond the surface of the needle shank. As the needles travel down the slope of the stitch cam, there is the possible difliculty (which sometimes happens) of the needle latch catching or trapping the nylon base yarn in the previous stitch that is protruding from the needle shank, causing a partial tuck loop, resulting in unsatisfactory knitting results and broken filaments.

From the above description of conventional floating system, it can be understood that in that system there is a minimum limitation as to the degree of tension that can be used on the spandex for satisfactory floating and a maximum limitation on the length of the nylon stitch. Thus a combination of these two factors limits the stretch range of the fabric between the minimum length dimensions and its maximum stretch dimensions.

With the fluid or air jet principle of the present invention, the two limitations just referred to can be overcome since the length of spandex per stitch can be controlled by a combination of applied tension on the thread line from the spandex package to the needle and fluid pressure that is used to position the yarn inside the needle circle. By this system substantially less tension is applied to the spandex yarn thereby reducing the contraction of that yarn around the needle shank when the sinker tension is removed from the stitch. Under the same condition, by reducing the protrusion of the base nylon yarn and obtaining a greater knitted stitch length of the base nylon yarn, it is possible to reduce the overall coursing in the knitted article, if so desired.

It has been demonstrated with the fluid or air jet principle of this invention, using the same spandex yarn, that the resulting fabric contains spandex which has 180% of its total 200% stretch left in the stitch length after the fabric is knitted (compared to of its total 200% left in the conventional float system).

The applicability of the fluid or air jet principle of the present invention to womens stockings and panty hose will be appreciated from the following discussion directed toward ladies stockings or panty hose knitting machines of current design, i.e. 3%" to 4" diameter cylinder of knitting needles. The objective currently is to produce compressive garments, especially panty hose or panty portions of panty hose, that will have some type of support or compression tensioning. If spandex yarn is applied to conventional jersey stitch along with nylon yarn the majority of the compression is distributed equally horizontally and vertically causing some difliculty with the panty hose garment tending to slip or ride down in the back. Knitting spandex in one jersey loop and floating across 2 or 3 needles before the next jersey loop is knitted produces the maximum compressive force in the horizontal direction. When obtaining the maximum compressive force in the horizontal direction by knitting one jersey stitch and floating intervening stitches, it has to be recognized that the length of spandex in this particular course must be of sufficient length so that it will not be stretched beyond its maximum elongation before the maximum elongation of the base fabric stitches is reached. An advantage of the air jet is to be able to introduce more spandex yarn per course even though only jersey stitches were formed on only /3 of the total number of needles. This length would be greater than could be placed in this course by the conventional float system.

Based on previously known defects in conventional float, it can be well understood that some tensioning has to be applied to the spandex yarn between the package and the needle to obtain the necessary compressive power desired. As an example, if an all jersey fabric were produced using nylon as the base yarn and spandex as the compressive or stretch yarn, and the length of spandex were identical to the length of nylon base yarn, there would be little, if any, force necessary to distort this type fabric from its limp dimensions.

The fluid or air jet principle of the present invention will be seen to overcome the inability of obtaining sufficient length of yarn per course of spandex immediately below the crotch area in the leg of ladies panty hose. Since the maximum girth of the maximum size wearer of panty hose at the thigh area could be as high as 24" in circumference whereas the maximum hip circumference would be 42" or less, if the same compressive force were used throughout knitting of the welt or panty portion and suflicient compression obtained in the hip area, then entirely too much compression would be obtained below the crotch area at the maximum thigh girth. Therefore, it is important to be able to position the correct length of spandex yarn per course whether it is knitted either in the complete jersey stitch or jersey stitch and floated combination so that virtually any desired power of compression can be obtained depending at what point the garment is worn with reference to the stress developed in the spandex yarn (i.e., at what place the wearing elongation is located with reference to the point on the stressstrain curve).

It thus will be seen that the objects of this invention have been fully and eifectively accomplished. It will be realized, however, that the foregoing specific embodiment has been shown and described only for the purpose of illustrating the principles of this invention and is subject to extensive change without departure from such principles. Therefore, this invention includes all modifications encompassed within the spirit and scope of the following claims.

What is claimed is:

1. In a method of knitting a compressive stretch garment on the needles of a circular knitting machine using first and second elastic stretch yarns with said second yarn being heavier and having a higher stretch potential than said first yarn, the steps including:

feeding said first yarn to the needles of said machine with a predetermined tension, knitting a plurality of courses of said first yarn to form a portion of said garment, feeding said second yarn at a tension lower than said predetermined tension to preselected spaced needles of said machine in preselected courses of said first yarn and floating said second yarn across at least one needle between said preselected spaced needles so that said second yarn will be floated across at least one stitch loop of said first yarn and will substantially coincide with other stitch loops of said first yarn,

the improvement comprising subsequent to the feeding of said second yarn to the preselected spaced needles, the step of directing a flow of air at a relatively low pressure from a source located outside the circle of needles radially inwardly of the circle at said preselected spaced needles while knitting and floating said second yarn into a said preselected course of said first yarn so that the floated portion of said second yarn will be disposed out of contact with said at least one needle.

2. The method defined in claim 1 wherein said first yarn is a synthetic linear thermoplastic polyamide and said second yarn is a non-foam elastomeric polyurethane.

3. The method defined in claim 1 wherein each course containing said second yarn the latter has stitch loops in every third wale and floats across the intermediate wales.

4. The method defined in claim 3 wherein said second yarn is arranged in alternate courses of said first yarn.

5. In a circular knitting machine having a yarn feeding station for feeding a first and a second type of elastic stretch yarn, means including a plurality of needles spaced about a circle for knitting said first yarn in a plurality of courses to define a portion of a garment, means including preselected spaced ones of said needles for knitting said second yarn into preselected ones of said courses wherein said second yarn will include stitch loops in some of the wales of said first yarn and portions which float across some needles between said preselected spaced ones of said needles corresponding to others of said wales of said first yarn, the improvement which comprises means located exteriorly of said circle of needles and spaced from said yarn feeding station for blowing a pressurized fluid at said preselected ones of said needles so that said portions of said second yarn which float across said some needles will be disposed inwardly of said circle in the form of an are extending between said preselected ones of said needles.

6. The structure defined in claim 5 wherein said fluid pressure is air at a gauge pressure of about 8 pounds per square inch.

7. The circular knitting machine as claimed in claim 5 wherein said needles are mounted for reciprocating movement in a predetermined direction and said means for blowing a pressurized fluid is positioned to direct the fluid in a direction generally transverse to said direction of movement of said needles.

References Cited UNITED STATES PATENTS 2,974,508 3/1961 Westmoreland 66-194 3,021,698 2/1962 Hill 669 B 3,511,064 5/1970 Major et al 66125 R 3,115,024 12/1963 Walrabenstein 669 R X 2,789,422 4/1957 Mills 66136 3,487,662 1/1970 Safrit et a1. 66177 X 3,016,726 1/1962 Lawson 66177 FOREIGN PATENTS 1,069,813 11/1959 Germany 66125 R 926,857 5/1963 Great Britain 66125 R 597,024 8/1959 Italy 66125 R 468,495 3/1969 Switzerland 66194 WILLIAM CARTER REYNOLDS, Primary Examiner US. Cl. X.R. 

